1. Technical Field
The present invention relates to a tire rubber composition, and more specifically, to a tire rubber composition blended with an antioxidant that is derived from a raw material other than petroleum resources, the tire rubber composition being capable of achieving an oxidation resistance equal to or higher than a conventional level and of improving forming processability and a low hysteresis loss property.
2. Description of the Related Art
Developments of pneumatic tires with higher performances and higher functions have heretofore been conducted by using mainly tire materials derived from petroleum resources. However, in order to solve problems including depletion of the petroleum resources, carbon dioxide emission control, and so forth, there has been a demand for development of pneumatic tires having increased proportions of tire materials that are not derived from the petroleum resources and having improved fuel efficiency so as to reduce carbon dioxide emission.
Nevertheless, there is a problem that it is difficult to ensure conventional tire performances simply by using the tire materials not derived from the petroleum resources. In particular, most of antioxidants used in tire rubber compositions are derived from the petroleum resources and it has been difficult to obtain a sufficient oxidation resistance by using antioxidants derived from raw materials other than the petroleum resources because such antioxidants lack affinity for rubber components.
For example, Japanese patent application Kokai publication No. Hei 9-296078 proposes the use of ascorbic acid (vitamin C) and tocopherol (vitamin E) in a tire rubber composition as antioxidants derived from raw materials other than the petroleum resources. However, when the antioxidants derived from the petroleum resources are completely replaced by these chemical compounds, rubber compositions with these chemical compounds cannot achieve oxidation resistance equivalent or superior to those with the conventional antioxidants. In addition, these chemical compounds may deteriorate forming processability because of the shorter scorch time of the resultant tire rubber composition.
Moreover, a rubber composition with these chemical compounds cannot achieve reduction in a hysteresis loss (or tan δ) for improving fuel efficiency as compared to a case of using an antioxidant derived from the petroleum resources.